Method of producing sizing agent-applied carbon fiber bundles

ABSTRACT

A method of producing sizing agent-applied carbon fiber bundles includes a sizing agent application process of immersing a plurality of carbon fiber bundles running side by side in a sizing agent bath, followed by a dry process performed to obtain sizing agent-applied carbon fiber bundles and, to address issues of wrapping of a carbon fiber bundle caused by sticking of a sizing agent solution to a guide roller, the first guide roller for the carbon fiber bundles after being immersed in the sizing agent bath and coming out of a liquid surface of the sizing agent bath is set to have a surface adhesive force of 0.2 N/cm2 or less.

TECHNICAL FIELD

This disclosure relates to a method of producing sizing agent-appliedcarbon fiber bundles having a sizing agent applied thereto.

BACKGROUND

A carbon fiber bundle should have excellent mechanical properties,particularly high specific strength and a high specific modulus ofelasticity so that the carbon fiber bundle can be widely used for, forexample, aerial or cosmic applications, sport and leisure applications,and general industrial applications such as automobiles and windmills.In recent years, consumers who use carbon fiber bundles strongly requirehigh-quality and cost-cutting of the carbon fiber bundles.

The carbon fiber bundle generally has low elongation and a brittleproperty, and easily generates fuzz and sometimes breakage by, forexample, contacting with a roller or rubbing with a guide in ahigh-order process. A general countermeasure against these problems isapplying various sizing agents to the carbon fiber bundle to impartbetter handling ability, improve the convergence and rubbing resistanceof the carbon fiber bundle, and suppress generation of fuzz of thecarbon fiber bundle so that the grade of the carbon fiber bundle ismaintained.

There are various methods of applying a sizing agent to the carbon fiberbundle such as spray jetting, dripping, kiss-roller coating and so on.In view of efficiency of simultaneous and easy application of a sizingagent to multiple carbon fiber bundles, dipping is preferable in whichthe carbon fiber bundles are immersed in a sizing agent bath. A processfor multiple carbon fiber bundles or high-speed production for costcutting, however, increases the amount of a sizing agent solutionattached to the carbon fiber bundles and taken out from the sizing agentbath and also increases the amount of the sizing agent solution attachedto a guide roller to guide the carbon fiber bundles to a dry processfollowing the sizing agent application process. Then, the sizing agentsolution is dried on a surface of the guide roller resulting ingeneration of a resin rich area and thus increase the viscosity of thesurface. A carbon fiber bundle brought into contact with the resin richarea generates fuzz and sometimes wraps around the guide roller, causinga problem of decreasing the process stability. Further, when the pitchbetween adjacent carbon fiber bundles is decreased to perform theprocess for multiple carbon fiber bundles, a coating layer formed by thesizing agent solution is easily generated between the adjacent carbonfiber bundles. Then, this liquid coating layer is directly driedresulting in unevenness of the sizing agent solution attached thereto.Further, the carbon fiber bundles that adjacently run stick to eachother due to the surface tension of the sizing agent solution and easilycause a problem of poor yarn separation.

As an improvement technique, Japanese Patent Laid-open Publication No.2013-23785 and Japanese Patent Laid-open Publication No. 07-145549disclose a method of removing a liquid coating layer, which is formed ofa sizing agent generated between carbon fiber bundles, by spraying apressurized gas toward the carbon fiber bundles that have come out of aliquid surface of a sizing agent bath.

Japanese Patent Laid-open Publication No. 2011-256486 discloses a methodof holding carbon fiber bundles with at least a pair of nip rollers toremove an excessive sizing agent solution that has been impregnated intothe carbon fiber bundles and applying a sizing agent solution to asurface(s) of the nip roller(s) to prevent drying of the sizing agentsolution on the nip rollers. Further, Japanese Patent Laid-openPublication No. 01-292038 discloses a method of producing carbon fiberbundles having excellent spreadability, the method including sizingnever-twisted carbon fiber bundles and then drying the carbon fiberbundles with a hot roller, in which wipe cloth is pressed against thehot roller to remove an excessive sizing agent solution from the hotroller.

With the methods of Japanese Patent Laid-open Publication No. 2013-23785and Japanese Patent Laid-open Publication No. 07-145549, even though itis possible to remove the liquid coating layer between the carbon fiberbundles, the carbon fiber bundles still have a sizing agent solutionattached thereto to transfer to a surface of a guide roller, causing aproblem of generating a resin rich area. In the method of JapanesePatent Laid-open Publication No. 2011-256486, the brittle carbon fiberbundles are held by the nip rollers resulting in generation of fuzz,causing a problem of decreasing the process stability. In the method ofJapanese Patent Laid-open Publication No. 01-292038, the excessivesizing agent solution attached onto the hot roller is removed with thewipe cloth to suppress a resin rich area formed by drying of the sizingagent solution on the hot roller itself, but the sizing agent solutionis easily dried on a guide roller located before the hot roller butfirst after the sizing agent application process, and a filament of thecarbon fiber bundles is stuck in a resin rich area generated during thedrying of the sizing agent solution, causing a problem of generatingfuzz or wrapping.

It could therefore be helpful to provide a method of producing sizingagent-applied carbon fiber bundles capable of solving the problems ofwrapping and fuzz of a carbon fiber bundle caused by the drying or theresin rich area of the sizing agent solution on the guide roller.

SUMMARY

We provide a method of producing sizing agent-applied carbon fiberbundles, the method including a sizing agent application process ofimmersing a plurality of carbon fiber bundles running side by side in asizing agent bath, followed by a dry process performed to obtain sizingagent-applied carbon fiber bundles, wherein the first guide roller forthe carbon fiber bundles after being immersed in the sizing agent bathand coming out of a liquid surface of the sizing agent bath has asurface adhesive force of 0.2 N/cm² or less.

The method of producing sizing agent-applied carbon fiber bundles havinga sizing agent solution applied thereto prevents drying and a resin richarea of the sizing agent solution on a guide roller and is thus capableof obtaining high grade carbon fiber bundles with less fuzz. The methodis also capable of suppressing wrapping of a carbon fiber bundle on theguide roller and is excellent in process stability.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic configuration diagram illustrating one exampleof a sizing process.

FIG. 2 shows a schematic configuration diagram illustrating anotherexample of the sizing process.

FIG. 3 shows a schematic configuration diagram illustrating anotherexample of the sizing process.

FIG. 4 shows a schematic configuration diagram illustrating anotherexample of the sizing process.

FIG. 5 shows a diagram illustrating a method of calculating force withwhich a carbon fiber bundle starts to move.

FIG. 6 shows a schematic configuration diagram illustrating one exampleof a conventional sizing process.

DESCRIPTION OF REFERENCE SIGNS

-   -   1: Carbon fiber bundle    -   2: Dipping roller    -   3: Guide roller    -   4: Sizing agent bath    -   5: Contacting object    -   6: Sizing agent solution spray means    -   7: Load measuring apparatus    -   8: Sizing agent bath different from sizing agent bath 4

DETAILED DESCRIPTION

A method of producing sizing agent-applied carbon fiber bundles obtainssizing agent-applied carbon fiber bundles through a sizing agentapplication process of immersing a plurality of carbon fiber bundlesrunning side by side in a sizing agent bath, and a dry process providedafter the sizing agent application process. The first guide roller forthe carbon fiber bundles after being immersed in the sizing agent bathand coming out of a liquid surface of the sizing agent bath has asurface adhesive force of 0.2 N/cm² or less.

Hereinafter, described in detail is the method of producing sizingagent-applied carbon fiber bundles.

A carbon fiber bundle may be one made of any of, for example, apitch-based raw material, a rayon-based raw material, and apolyacrylonitrile-based raw material, but a polyacrylonitrile-basedcarbon fiber bundle is preferable from viewpoints of quality andproductivity. The form of the carbon fiber bundle is not alsoparticularly limited, and it is possible to use, for example, a carbonfiber bundle having a filament diameter of 3 μm or more and 10 μm orless. The number of carbon fiber filaments constituting the carbon fiberbundle is not also particularly limited, and can be, for example, 1000to 100000. The desired effects, however, are easily achieved when thecarbon fiber bundle includes a relatively large number of filaments,3000 filaments or more that take a large amount of a sizing agentsolution from the sizing agent bath.

The polyacrylonitrile-based carbon fiber bundle preferably used can beobtained by a known method that includes oxidizing, pre-carbonizing, andcarbonizing a polyacrylonitrile-based precursor fiber bundle, and thepolyacrylonitrile-based carbon fiber bundle is not particularly limited.Oxidation can be performed at 200 to 300° C. in an oxidizing atmosphere.As an oxidizing gas in the oxidation, air is preferable from aneconomical viewpoint. Subsequently, pre-carbonization can be performedin an inert atmosphere and in a pre-carbonization furnace at a maximumtemperature of 300 to 1000° C. Further, the pre-carbonized fiber bundleis carbonized at a maximum temperature of 1200 to 2000° C. to obtain acarbon fiber bundle. The carbon fiber bundle may further be graphitizedat a temperature of 2000 to 3000° C. as necessary. Thepre-carbonization, the carbonization, and the graphitization areperformed in an inert atmosphere. A used inert gas is, for example,nitrogen, argon, or xenon, and nitrogen is preferably used from theeconomical viewpoint.

When the carbon fiber bundle is made into carbon fiber reinforcedcomposites, the carbon fiber bundle is preferably subjected to a surfacetreatment such as an electrolytic oxidation treatment performed in anelectrolyte, or an oxidation treatment in a gas phase or a liquid phase,to easily improve the affinity or the adhesive property between thecarbon fiber bundle and a matrix resin. As the electrolyte, both anacidic aqueous solution and an alkaline aqueous solution are usable. Asthe acidic aqueous solution, sulfuric acid or nitric acid having strongacidity is preferable. As the alkaline aqueous solution, preferably usedis an aqueous solution of an inorganic alkali such as ammoniumcarbonate, ammonium hydrogen carbonate, or ammonium bicarbonate.

As the sizing agent solution, it is possible to use one obtained bydispersing or dissolving a sizing agent in water or an organic solventsuch as acetone. From viewpoints of uniform application to the carbonfiber bundles and safety, an aqueous dispersion or an aqueous solutionis preferable that is obtained by dispersing or dissolving a sizingagent in water. As the sizing agent, it is possible to use one of sizingagents known in a field of a carbon fiber, according to the matrix resinused in a high-order process. The sizing agent can contain a main agentand various additives described later, and can be formed of, forexample, the main agent and an emulsifier. It is possible to obtainsizing agent-applied carbon fiber bundles having the sizing agentapplied to surfaces thereof by drying carbon fiber bundles impregnatedwith this sizing agent solution.

The type of the sizing agent is not particularly limited, but iseffective against a sizing agent solution that is dried on the guideroller resulting in generation of a resin rich area and thus easilyforms adhesive attached substances. When the sizing agent contains athermoset resin as a component, possibly used as the main component ofthe sizing agent is, for example, an epoxy resin, an epoxy-modifiedpolyurethane resin, a polyester resin, a phenolic resin, a polyamideresin, a polyurethane resin, a polycarbonate resin, a polyetherimideresin, a polyamide imide resin, a polyimide resin, a bismaleimide resin,a urethane-modified epoxy resin, a polyvinyl alcohol resin, a polyvinylpyrrolidone resin, a polyethersulfone resin, or a combination of two ormore of these resins. Alternatively, when the sizing agent contains athermoplastic resin as a component, possibly used as the main componentof the sizing is one containing at least a single component or aplurality of components selected from the group of polycarbonate,polypropylene, polyethylene, polystyrene, polyethylene terephthalate,polyvinyl alcohol, polyvinyl pyrrolidone, polyethylene glycol,polyethylene imine, polyacrylamide, polyphenylene ether, polyacetal,polybutylene terephthalate, polyphenylene sulfide, polyether etherketone, an elastomer cellulose compound, an acrylic resin, apolyurethane resin, a polyamide resin, a fluorine resin, an ABS resin, aliquid crystal polymer, and a styrene-maleic anhydride copolymer(partially) neutralized with sodium hydroxide.

These organic compounds are mostly insoluble in water and, therefore,may be formed into an emulsion by adding a surfactant to these organiccompounds. The type of the surfactant is not particularly limited, but anonionic surfactant is preferably used. Examples of the nonionicsurfactant include ether compounds such as polyoxyethylene alkyl ether,single chain polyoxyethylene alkyl ether, polyoxyethylene secondaryalcohol ether, polyoxyethylene alkyl phenyl ether, polyoxyethylenesterol ether, polyoxyethylene sterol ether, a polyoxyethylene lanolinderivative, an ethylene oxide derivative of an alkyl phenol formalincondensate, and polyoxyethylene polyoxypropylene alkyl ether; etherester compounds such as polyoxyethylene glycerin fatty acid ester,polyoxyethylene castor oil or hydrogenated castor oil, polyoxyethylenesorbitan fatty acid ester, and polyoxyethylene sorbitol fatty acidester; and ester compounds such as polyethylene glycol fatty acid esterand polyglycerin fatty acid ester. From among these compounds, one orseveral compounds in combination are used.

Dilution to form the sizing agent solution is preferably performed usingeconomical and safe water. When the sizing agent solution is arranged asan aqueous dispersion, adjustment is made so that the sizing agent is ina concentration range allowing water to be present as a continuousphase. A general method includes diluting the sizing agent to give asizing agent concentration of about 0.1 to 10 mass % in the sizing agentbath so that the amount of the sizing agent attached to the carbon fiberbundles becomes a desired amount, and impregnating the carbon fiberbundles with the sizing agent solution. When water is added to dilutethe sizing agent solution for adjustment of the concentration in thesizing agent bath to a desired concentration, the dilution may beperformed once or a plurality of times depending on the compositionconcentration of, for example, the main component other than water inthe sizing agent solution. The sizing agent solution may also contain,in addition to the main component, various additives such as asurfactant, a smoothing agent, and an emulsifier.

As regards a resin rich area of the sizing agent solution generated onthe guide roller along a running course of the carbon fiber bundlesafter the carbon fiber bundles pass the sizing agent applicationprocess, the resin rich area is generated as follows: the sizing agentsolution taken out by the carbon fiber bundles from the sizing agentbath is transferred, retained, and dried on the guide roller. Generationof the resin rich area due to the drying of the resin of the sizingagent solution on the guide roller brings a running carbon fiber bundleinto contact with the resin rich area on the guide roller resulting inthe adhesiveness at the time of separation of the carbon fiber bundlefrom the resin rich area increased, and thus generates, for example,fuzz or wrapping. The method of producing carbon fiber bundles iscapable of preventing the drying of the sizing agent solution on theguide roller and preventing the resin rich area of the sizing agent bymaking the first guide roller for the carbon fiber bundles after beingimmersed in the sizing agent bath and coming out of a liquid surface ofthe sizing agent bath to have a surface adhesive force of 0.2 N/cm² orless, preferably 0.1 N/cm² or less. The guide roller having a surfaceadhesive force of more than 0.2 N/cm² allows a carbon fiber bundle togenerate fuzz, sometimes causing the problem of wrapping. The guideroller retains a surface adhesive force of preferably 0.20 N/cm² orless, further preferably 0.10 N/cm² or less. With the guide rollerhaving a lower surface adhesive force, the carbon fiber bundles have ahigher grade to thus obtain high grade carbon fiber bundles with lessfuzz by preventing the drying and the resin rich area of the sizingagent solution on the guide roller, whereas it is necessary to apply thesizing agent to the carbon fiber bundles. Then, not a little amount ofthe sizing agent solution is dried and forms the resin rich area on theguide roller to make the guide roller adhesive. Therefore, the guideroller does not substantially have a surface adhesive force of zero, andthe guide roller preferably has a surface adhesive force of 0.01 N/cm²as a lower limit.

The surface adhesive force of the guide roller is calculated by thefollowing equation. Surface adhesive force of guide roller (N/cm²)=forcewith which carbon fiber bundle starts to move/contacting surface area ofcarbon fiber bundle with guide roller

A method of calculating the force with which the carbon fiber bundlestarts to move is described with reference to FIG. 5. The force withwhich the carbon fiber starts to move is measured as follows within 10minutes after a stop of a facility for producing carbon fiber bundles atthe time of long-term stable production, and the measured value isregarded as a value during the production.

First, a guide roller 3 having a sizing agent solution attached theretois fixed to not be rotated, and then a carbon fiber bundle 1 that isabout to be subjected to application of a sizing agent and is absolutelydry is hung, with a contact angle of 180°, from a most upper point ofthe guide roller 3. Next, a ring is made at one end of the carbon fiberbundle 1 hung around the circumference of the guide roller 3, a hook isattached to a tip of a load measuring apparatus 7, and the hook ishooked to the ring of the carbon fiber bundle. The load measuringapparatus is not particularly limited, but preferred is a push-pullgauge capable of measuring an instantaneous maximum load. The carbonfiber bundle is slowly pulled with the load measuring apparatus, and themaximum force right before the carbon fiber bundle 1 starts to move onthe surface of the guide roller 3 is defined as the force with which thecarbon fiber starts to move (the unit is Newton).

In the meantime, the “at the time of long-term stable production” refersto period during which the carbon fiber bundles are continuouslyproduced industrially stably for a long period (24 hours or longer)without fuzz and wrapping. The “stop of the facility for producingcarbon fiber bundles” refers to a moment of stopping the facility forproducing carbon fiber bundles that serves the process from the sizingagent bath to the guide roller. It is possible to measure the force withwhich the carbon fiber bundle starts to move only by fixing the guideroller through stopping the facility for producing carbon fiber bundles.

The force with which the carbon fiber bundle starts to move isadjustable by adjusting the dryness of the sizing agent solutionattached to the surface of the guide roller or by changing the materialfor the guide roller.

The contacting surface area of the carbon fiber bundle with the guideroller is calculated by a product of the circumferential length alongthe circumference of the surface of the guide roller between a point atwhich the carbon fiber bundle starts to be brought into contact with theguide roller and a point at which the carbon fiber bundle is separatedfrom the guide roller and the width of the carbon fiber bundle. It ispossible to change the contacting surface area by changing, for example,the circumferential length on the guide roller in contact with thecarbon fiber or the number of filaments in the carbon fiber bundle.

Next, our methods are described in further detail with reference todrawings.

FIG. 1 shows a schematic configuration diagram illustrating one exampleof a sizing process. In the example illustrated in FIG. 1, carbon fiberbundles 1 pass a dipping roller 2 to be immersed in a sizing agent bath4, is taken out from a liquid surface by a guide roller 3, and is leadto a next process, or a dry process following the sizing process. Insuch an example, the carbon fiber bundles 1 having a sizing agentsolution applied thereto pass the guide roller 3 to attach the sizingagent solution to the guide roller 3. To prevent sticking of the sizingagent solution attached to the guide roller 3, at least one contactingobject 5 selected from cloth and elastic materials such as a resin andrubber is brought into contact with the guide roller 3. The contactingobject 5 wipes the sizing agent solution attached to the guide roller toadjust the surface adhesive force of the guide roller, enabling theguide roller to have a surface adhesive force of 0.2 N/cm² or less.

A method of bringing the contacting object into contact with the guideroller is not particularly limited, and is, for example, a method ofuniformly pressing the contacting object against the guide roller. Thecontacting object to be pressed is made of any material such as cloth,flannel, an elastic material such as a resin or rubber, or a metal aslong as the material is capable of removing the sizing agent solutionattached to the guide roller and enables the guide roller to have asurface adhesive force of 0.2 N/cm² or less. Particularly, in terms of aproperty of being less likely to generate static electricity, toughness,and water absorbability, thick flat-woven cotton cloth represented bycalico, or flannel such as long-pile cotton flannel or wool fabric isoptimal in respect of the effect of removing the sizing agent solution.

The pressure applied to the contacting object is not particularlylimited as long as the contacting object is capable of removing thesizing agent solution attached to the guide roller, and the dispositionstate of the contacting object can be either fixation or rotation. Whenthe applied pressure is low, the removal of the sizing agent solution isinsufficient and so the effect decreases, whereas when the appliedpressure is excessively high, the guide roller is not rotated and thus alot of fuzz of a running carbon fiber bundle is generated by rubbing,allowing wrapping of the carbon fiber bundle on the guide roller todecrease the process stability. Therefore, a cloth contacting object ispreferably rotatable while wrapped around the guide roller. Further, aposition of the contacting object to which the guide roller is pressedis not particularly limited, but the contacting object is preferablypressed on a surface of the guide roller in no contact with the runningcarbon fiber bundles, in terms of preventing generation of fuzz andbreakage of a running carbon fiber bundle caused by contact between thecontacting object and the carbon fiber bundles.

Further, when an elastic material or a metal is pressed against theguide roller, the elastic material or the metal is preferably formedinto a sharp shape such as a scraper, which is, however, not too sharpto damage the guide roller, in terms of removal efficiency of the sizingagent solution. When the scraper is used, the scraper is set to becapable of holding back, during rotation of the guide roller, the sizingagent solution transferred onto the surface of the guide roller, with asharp tip portion of the scraper in contact with the guide roller.Further, to hold back, with the scraper, the sizing agent solutionefficiently against the whole surface of the guide roller, the scraperis preferably set to allow the sharp tip portion of the scraper to be inlinear contact with the guide roller in parallel with a shaft directionof the guide roller. The sharp portion of the scraper is preferably ahard scraper blade made of a metal or plastic, and such a sharp portionis capable of uniformly removing solid attached substances or adhesiveattached substances such as the resin rich area generated on the guideroller during the drying of the sizing agent solution. Further, toremove, with the scraper, the sizing agent solution across the fullwidth direction of the guide roller, the scraper may be set along theshaft direction of the guide roller, with guide means such as a guiderail for the scraper blade, provided in parallel with the shaft of theguide roller. This configuration enables efficient removal of the solidattached substances or the adhesive attached substances on the guideroller.

FIG. 2 shows a schematic configuration diagram illustrating anotherexample of the sizing process. In the example illustrated in FIG. 2,carbon fiber bundles 1 pass a dipping roller 2 to be immersed in asizing agent bath 4, are taken out from a liquid surface by a guideroller 3, and are lead to a next process, or a dry process following thesizing process. Also in this example, the carbon fiber bundles 1 havinga sizing agent solution applied thereto pass the guide roller 3 toattach the sizing agent solution to the guide roller 3. Therefore, toprevent sticking of the sizing agent attached to the guide roller 3, asizing agent solution different from the sizing agent solution in thesizing agent bath 4 is applied to the guide roller 3 with use of, forexample, sizing agent solution spray means 6. A method of applying thesizing agent solution is not particularly limited to the sizing agentsolution spray means 6, and is, for example, a method of dripping orspraying the sizing agent solution to the whole surface of the guideroller, or a method of immersing the guide roller in the sizing agentsolution. In such an example, there is no problem as long as the sizingagent solution is applied so that the guide roller is not dried and theguide roller is allowed to have a surface adhesive force of 0.2 N cm² orless, and no particular limitation is provided unless the sizing agentsolution is retained and dried on the surface of the guide rollerresulting in generation of the resin rich area.

For example, as illustrated in FIG. 2, the disposition of the sizingagent solution spray means 6 above the guide roller 3 and the spray ofthe sizing agent solution from the sizing agent solution spray means 6are capable of sufficiently suppressing the drying of the sizing agentsolution on the guide roller 3. An upper limit of the spraying amount ofthe sizing agent solution per one hour sprayed from the sizing agentsolution spray means 6 is not particularly limited because the guideroller 3 only has to be wet, but the upper limit is preferably 50 to 130mg/cm²/hr, more preferably 80 to 100 mg/cm²/hr. The sizing agentsolution in a spraying amount per one hour of less than 50 mg/cm²/hr issometimes evaporated on the guide roller 3, generating the resin richarea and resulting in generating fuzz or wrapping of a carbon fiberbundle. The sizing agent solution in a spraying amount per one hour ofmore than 130 mg/cm²/hr means use of an excessive amount of the sizingagent solution and thus is disadvantageous in terms of costs.

Further, as illustrated in FIG. 3, immersing of the guide roller 3 in asizing agent bath 8 different from the sizing agent bath used in thesizing process is also capable of sufficiently suppressing the drying ofthe sizing agent solution on the guide roller 3.

The sizing agent solution separately applied to the guide roller as inthe examples illustrated in FIGS. 2 and 3 is not particularly limited,but preferably causes no change to the composition and the amount of thesizing agent applied to the carbon fiber bundles obtained and ispreferably identical with the sizing agent solution for immersing thecarbon fiber bundles.

In the meantime, more effect is exerted by combining the method ofbringing the contacting object into contact with the guide roller andthe method of applying a sizing agent solution separately from thesizing agent bath 4. For example, as illustrated in FIG. 4, the spray ofthe sizing agent solution from the sizing agent solution spray means 6to the guide roller 3, followed by pressing the contacting objectagainst the guide roller prevents sticking of the sizing agent solutionand removes an excessive sizing agent solution to be capable ofadjusting the surface adhesive force of the guide roller to theprescribed range, more securely than employing only the method ofpressing the contacting object against the guide roller.

Further, when the carbon fiber bundles 1 pass the dipping roller 2 to beimmersed in the sizing agent bath 4, are taken out from the liquidsurface by the guide roller 3, and are lead to the next process, or thedry process following the sizing process, a water-resistant guide rolleris preferably used as the guide roller 3 to not allow generation of theresin rich area on the guide roller 3 caused by the sizing agentsolution. Specific examples of the water-resistant guide roller includea fluororesin and stainless steel (SUS). Particularly, stainless steel(SUS) that is less likely to cause rust is more preferable because thecarbon fiber bundles having the sizing agent solution applied theretorun on the guide roller to always make the surface of the guide rollerwet. Examples of the type of stainless steel include SUS304, SUS304L,SUS316, and SUS316L.

In the production method, a sizing agent liquid coating layer betweenadjacent carbon fiber bundles is easily formed in a place between aposition where the carbon fiber bundles come out of the liquid surfaceafter immersed in the sizing agent solution and a guide roller withwhich the carbon fiber bundles is first brought into contact, and in aplace between the guide roller and before the dry process. The sizingagent liquid coating layer can be formed by an excessive sizing agentsolution taken out by the carbon fiber bundles immersed in the sizingagent bath or by the above-described sizing agent solution applied tothe guide roller separately from the sizing agent solution in the sizingagent bath. Formation of the sizing agent liquid coating layer betweenadjacent carbon fiber bundles brings the adjacent carbon fiber bundlesinto contact with each other due to the surface tension of the sizingagent liquid coating layer resulting in generation of fuzz or increaseof unevenness in sizing agent amount, dryness, or in color of the carbonfiber bundles obtained. Therefore, the sizing agent liquid coating layeris preferably removed in each of the places. A method of removing thesizing agent liquid coating layer is not particularly limited, and is,for example, spraying a pressurized gas, application of vibration,application of ultrasonic waves, or physical contact by disposing aguide. Among these methods, a non-contact method is preferable that iscapable of easily preventing generation of fuzz of a carbon fiberbundle, and further, spraying a pressurized gas is more preferable froma viewpoint of reducing facility costs.

The tension of the carbon fiber bundles in the sizing agent applicationprocess is preferably 3.5 to 8.5 cN/tex. With the tension at 3.5 cN/texor more, it is possible to prevent a decrease in convergence of thecarbon fiber bundles. On the other hand, with the tension at 8.5 cN/texor less, it is possible to easily prevent generation of fuzz andbreakage of a carbon fiber bundle caused by tension application. Fromthe above viewpoints, the tension of the carbon fiber bundles in thesizing agent application process is preferably 3.5 to 8.5 cN/tex, morepreferably 4.0 to 8.0 cN/tex, further preferably 4.5 to 7.5 cN/tex. Thetension of the carbon fiber bundles in the sizing agent applicationprocess may be singly controlled only in the sizing agent applicationprocess or may be controlled together with the tension in the dryprocess by an identical mechanism. A method of controlling the tensionis not particularly limited, and is, for example, a method includingadjusting a ratio of driving speed between before and after the sizingagent application process. It is possible to know the process tension bymeasuring the tension of a running filament right before the applicationof the sizing agent solution with, for example, a tension meter, and toadjust the tension by, for example, rotary torque of a roller before andafter the application of the sizing agent solution.

The carbon fiber bundles having the sizing agent solution appliedthereto in the sizing agent application process is dried at about 200 to300° C. in the dry process and wound up around a paper tube. As a drymethod, it is possible to use a contact-type dryer such as a drum dryer,and a non-contact-type hot air dryer singly or in combination, and themethod is not particularly limited.

EXAMPLES

Our methods are further specifically described by way of examples and acomparative example. Evaluation items for the examples and thecomparative example were checked by the following evaluation methods.

Surface Adhesive Force of Guide Roller

The surface adhesive force of the guide roller was calculated by thefollowing equation. Surface adhesive force of roller (N/cm²)=force withwhich carbon fiber bundle starts to move/contacting surface area ofcarbon fiber bundle with guide roller

The force with which a carbon fiber bundle starts to move was measuredas follows in 5 minutes after a stop of a facility for producing carbonfiber bundles at the time of long-term stable production. That is, asillustrated in FIG. 5, a stainless steel guide roller 3 having a sizingagent solution attached thereto was fixed to not be rotated, and then acarbon fiber bundle 1 that was about to be subjected to application of asizing agent solution and was absolutely dry was hung, with a contactangle of 180°, from a most upper point of the guide roller 3.Thereafter, a ring was made at one end of the carbon fiber bundle 1. Asa load measuring apparatus 7, a digital push-pull gauge (RX series, itemNo. RX-10) manufactured by Aikoh Engineering Co., Ltd. was used. A gaugeattachment (item No. 011B), or a hook was attached to a tip of thedigital push-pull gauge, and the carbon fiber bundle 1 was slowly pulledalong the circumference of the guide roller 3 while the hook was kepthooked to the ring of the carbon fiber bundle 1. The maximum force rightbefore the carbon fiber bundle 1 started to move on the surface of theguide roller 3, that is, the force with which the carbon fiber bundlestarted to move was measured with the push-pull gauge.

The contacting surface area of the carbon fiber bundle with the guideroller was calculated by a product of the circumferential length of theguide roller in contact with the carbon fiber bundle and the width ofthe carbon fiber bundle.

Grade

As a grade of a sizing agent-applied carbon fiber bundle, visual fuzz ona side surface of a carbon fiber bundle packaged bobbin was observed andevaluated according to the following criteria.

⊙=fuzz of less than 5 fibers/100 mm²◯=fuzz of 5 fibers/100 mm² or more and less than 10 fibers/100 mm²x=fuzz of 10 fibers/100 mm² or more

Example 1

A sizing agent was applied to a plurality of carbon fiber bundlesrunning side by side in a facility having the configuration illustratedin FIG. 1, and the carbon fiber bundles were allowed to undergo a dryprocess to obtain sizing agent-applied carbon fiber bundles.

Specifically, carbon fiber bundles formed from polyacrylonitrile-basedprecursor fiber bundles and each included 3000 filaments were immersedin a sizing agent bath filled with a sizing agent solution containing,as a main component, an aromatic epoxy compound, or a bisphenol A epoxyresin at a concentration of 3 mass %, and were subsequently subjected tothe dry process to obtain sizing agent-applied carbon fiber bundles. Asthe guide roller 3 with which the carbon fiber bundles were firstbrought into contact after coming out of a liquid surface of the sizingagent, a guide roller made of stainless steel (SUS) was used, andlong-pile cotton flannel cloth was, as a contacting object 5, pressed ona lowermost portion of the guide roller 3.

The guide roller 3 had a surface adhesive force of 0.05 N/cm², and thevisual fuzz on the side surface of the carbon fiber bobbin was verygood. Table 1 shows the results.

Example 2

Sizing agent-applied carbon fiber bundles were obtained, with all theprocedures performed similarly to in Example 1 except that a scrapermade of plastic was used as the contacting object 5, in place of thelong-pile cotton flannel cloth. The guide roller 3 had a surfaceadhesive force of 0.07 N/cm², and the visual fuzz on the side surface ofthe carbon fiber bobbin was very good. Table 1 shows the results.

Example 3

Sizing agent-applied carbon fiber bundles were obtained, with all theprocedures performed similarly to in Example 1 except that the processillustrated in FIG. 2 was employed as the sizing agent applicationprocess. That is, all the procedures were performed similarly to inExample 1 except that a sizing agent solution was sprayed from above theguide roller 3 with which the carbon fiber bundles were first broughtinto contact after coming out of a liquid surface of the sizing agentand that the contacting object was removed. The spraying amount of thesizing agent solution per one hour at this time was 100 mg/cm²/hr. Theguide roller 3 had a surface adhesive force of 0.04 N/cm², and thevisual fuzz on the side surface of the carbon fiber bobbin was verygood. Table 1 shows the results.

Example 4

Carbon fiber bundles were obtained, with all the procedures performedsimilarly to in Example 3 except that the spraying amount of the sizingagent solution per one hour was changed to 80 mg/cm²/hr. The guideroller 3 had a surface adhesive force of 0.13 N/cm², and the visual fuzzon the side surface of the carbon fiber bobbin was good. Table 1 showsthe results.

Example 5

Sizing agent-applied carbon fiber bundles were obtained, with all theprocedures performed similarly to in Example 1 except that the processillustrated in FIG. 3 was employed as the sizing agent applicationprocess. That is, all the procedures were performed similarly to inExample 1 except that the guide roller 3 with which the carbon fiberbundles were first brought into contact after coming out of the liquidsurface of the sizing agent in Example 1 was immersed in anotherindependent sizing agent bath 8 and that the contacting object wasremoved. The guide roller 3 had a surface adhesive force of 0.08 N/cm²,and the visual fuzz on the side surface of the carbon fiber bobbin wasgood. Table 1 shows the results.

Example 6

Sizing agent-applied carbon fiber bundles were obtained, with all theprocedures performed similarly to in Example 1 except that the processillustrated in FIG. 4 was employed as the sizing agent applicationprocess. That is, the procedures were performed similarly to in Example1 except that a sizing agent solution was sprayed to the carbon fiberbundles sent out from the guide roller 3 at a spraying amount per onehour of 80 mg/cm²/hr. The guide roller 3 had a surface adhesive force of0.02 N/cm², and the visual fuzz on the side surface of the carbon fiberbobbin was very good. Table 1 shows the results.

Example 7

Sizing agent-applied carbon fiber bundles were obtained, with all theprocedures performed similarly to in Example 1 except that the sizingagent bath was filled with a sizing agent solution containing, as a maincomponent, polyurethane at a concentration of 2 mass %. The guide roller3 had a surface adhesive force of 0.06 N/cm², and the visual fuzz on theside surface of the carbon fiber bobbin was very good. Table 1 shows theresults.

Comparative Example 1

Sizing agent-applied carbon fiber bundles were obtained similarly to inExample 1 except that the process illustrated in FIG. 6 was employed asthe sizing agent application process. That is, the procedures wereperformed similarly to in Example 1 except that the cotton flannel clothas the contacting object was not pressed against the guide roller. As aresult, the sizing agent was dried on the guide roller resulting ingeneration of a resin rich area and thus increased the surface adhesiveforce of the guide roller 3 to as high as 0.25 N/cm², generating fuzz ofa running carbon fiber bundle and thus remarkably deteriorating thevisual fuzz on the side surface of the carbon fiber bobbin. Table 1shows the results.

TABLE 1 Comparative Example 1 Example 2 Example 3 Example 4 Example 5Example 6 Example 7 Example 1 Material for guide SUS SUS SUS SUS SUS SUSSUS SUS roller Contacting object Cotton Scraper None None None CottonCotton None flannel cloth flannel cloth flannel cloth Main component ofBisphenol A Bisphenol A Bisphenol A Bisphenol A Bisphenol A Bisphenol APolyurethane Bisphenol A sizing agent solution epoxy epoxy epoxy epoxyepoxy epoxy epoxy Spraying amount of None None 100 80 None 80 None Nonesizing agent solution per one hour [mg/cm²/hr] Immersion of guide NoneNone None None Performed None None None roller in sizing agent solutionSurface adhesive force 0.05 0.07 0.04 0.13 0.08 0.02 0.06 0.25 of guideroller [N/cm²] Fuzz grade* ⊙ ⊙ ⊙ ◯ ◯ ⊙ ⊙ X *Fuzz grade ⊙ = fuzz of lessthan 5 fibers/100 mm² ◯ = fuzz of 5 fibers/100 mm² or more and less than10 fibers/100 mm² X = fuzz of 10 fibers/100 mm² or more

1.-3. (canceled)
 4. A method of producing sizing agent-applied carbonfiber bundles, comprising: a sizing agent application process ofimmersing a plurality of carbon fiber bundles running side by side in asizing agent bath, followed by a dry process performed to obtain sizingagent-applied carbon fiber bundles, wherein the first guide roller forthe carbon fiber bundles after being immersed in the sizing agent bathand coming out of a liquid surface of the sizing agent bath has asurface adhesive force of 0.2 N/cm² or less.
 5. The method according toclaim 4, wherein a contacting object is brought into contact with theguide roller to allow the guide roller to have a surface adhesive forceof 0.2 N/cm² or less.
 6. The method according to claim 4, wherein asizing agent solution is further applied to the guide roller after thesizing agent application process to allow the guide roller to have asurface adhesive force of 0.2 N/cm² or less.